Spark suppression shield for electric motors

ABSTRACT

Spark suppression shield for electric motors relates to universal commutator motors and to permanent magnet DC motors operating in environment containing flammable or explosive gases. The collar shaped as a wall is extending from bearing frame and surrounding commutator in approximately it&#39;s total height, where the gap in radial direction between commutator and collar is up to 3 mm and the collar might or might not have collar openings.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of the filing of Slovene Patent Application No. P-201300083, filed Mar. 31, 2013, entitled “ Spark suppression shield for electric motors”, and the specifications and claims thereof are incorporated herein by reference.

FIELD OF INVENTION

The present invention relates to field of electric universal commutator motors and to permanent magnet DC motors operating in environment containing flammable or explosive gases.

BACKGROUND OF INVENTION

In all electrical motors containing commutator and brushes, contact between commutator and conductive brushes, is source of sparking. If such motor operates in environment containing flammable gases, it might lead to fire or even to explosion.

Well known solution to prevent explosion are totally sealed motors. First disadvantage of such solution is poor dissipation of heat. Consequentially, for same output power, larger and more expensive motor is needed. Second disadvantage is brush dust which remains inside the motor. Brush dust is conductive and could be reason for leakage current. Brush dust can be also reason for premature bearing failure.

Another solution to prevent explosion is described in Patent No.: U.S. Pat. No. 6,417,595 B1 which was applied by McMillan Electric Company. Main elements which provide protection are collar embracing commutator, seal on one said of commutator and labyrinth on other side of commutator. This solution is more cost effective as totally sealed motor.

SUMMARY OF THE INVENTION

Subject of the invention is new solution which enables operation of universal commutator motors and permanent magnet DC motors in environment containing flammable gases. There is a shield, in the form of collar, surrounding commutator in radial direction. Disadvantage of this protection is that brush dust gets trapped inside the collar. Openings in collar are introduced in order that brush dust can be drifted away from commutator and from bearing region. Openings are located in direction of rotation as far away as possible from brushes. This solution is simpler and more cost effective comparing to existing ones. Commutator is not totally sealed. Despite this it still enables explosion protection in accordance with standard UL1604, Section 10 and 11.5.

BRIEF DESCRIPTION OF THE DRAWINGS:

Drawing 1: General cross-sectional view,

Drawing 2: Perspective view of bearing frame with collar openings—opened type,

Drawing 3: Perspective view of bearing frame with collar openings—closed type,

Drawing 4: Perspective view & cross-sectional view of bearing frame with partially opened channels,

Drawing 5: Perspective view & cross-sectional view of bearing frame with totally closed channels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Main assembly parts are rotor 1 and bearing frame 2. Rotor 1 is supported by ball bearing 6, which is assembled in the bearing frame 2, and by bearing 8 at the opposite side of the axis. Brush assembly 4 is used to conducts electric current between stationary wires and commutator 3 which is fixed on rotor shaft 11. Brush assembly 4 consists of brush sleeve 41 and brush 42.

Spark protection shield is formed as a collar 5, surrounding commutator 3, might be integral part of bearing frame 2 or it could be separate assembly part. Collar 5 is a wall, extending from bearing frame 2 and surrounding commutator 3 in approximately it's total hight, i.e. including commutator hooks. Inner wall of collar might consist of 2 cylindrical surfaces of different diameters. Surface with smaller diameter 501 surrounds main body of commutator 3. Surface with larger diameter 502 surrounds commutator hooks 31. Gap in radial direction between commutator 3 and collar 5 is up to 3 mm. Collar 5 might or might not have collar openings 51, 52. Openings 51, 52 could be of different shapes. As presented on FIG. 2, opening 51 is of opened type, i.e. opening 51 spreads to the top of the collar 5. As presented on FIG. 3, opening 52 is of closed type, i.e. opening 52 is interrupted on the top of the collar 5, meaning that the collar 5 is integral on it's top. Total area of openings 51, 52 is up to 20% of commutator 3 active area. Commutator 3 active area is area which is actually in contact with brushes. Openings 51, 52 are positioned at angle from 90° to 175° away from brush in the direction of rotation of the rotor 1.

Collar openings 51, 52 might or might not be extended into channels 511, 512. Channels 511, 512 as presented in drawing 4 and 5, provide additional protection against sparking. Channel 511 is opened on the top. Channel 512 is on it's top covered with a wall, spreading from the top of the collar 5. Channels 511, 512 cross section area may rise from spark protection shield 5 to exhaust.

Even though collar is equipped with collar openings, carbon dust concentration near bearing 6 is significantly higher comparing to motors without collar. Despite the fact bearing 6 is equipped with sealing, carbon dust is still slightly penetrating into bearing and polluting bearing grease. It results in reduced life time of ball bearing 6. To prevent this, anti-dust washer 7, made of nonconductive material, is introduced. It is centered on the rotor shaft; its axial position is assured with ball bearing 6. 

1. Spark suppression shield for electric motors which relates to universal commutator motors and to permanent magnet DC motors operating in environment containing flammable or explosive gases, characterized by, that the there is the collar shaped as a wall, extending from bearing frame and surrounding commutator in approximately it's total hight, where the gap in radial direction between commutator and collar is up to 3 mm and the collar might or might not have collar openings.
 2. Spark suppression shield according to claim 1, where the total area of openings is up to 20% of commutator active area.
 3. Spark suppression shield according to claims 1 and 2, where the openings are positioned at angle from 90° to 175° away from brush in the direction of rotation of the rotor.
 4. Spark suppression shield according to previous claims, where the collar openings might or might not be extended into channels.
 5. Spark suppression shield according claim 4, where the channel is opened on the top.
 6. Spark suppression shield according claim 4, where the channel is on it's top covered with a wall, spreading from the top of the collar. 